The soil testing is not a simple task, as it is performed by a soil testing company which has the required expertise and equipment for determining the strength of soil. Buy the services of a reputable company and wait for them to process the soil samples in their laboratory.
The testing company will present a full documented report, and they will mention if the soil requires compaction or not. The first layer of construction material, common for all types of buildings, can be turned solid by pressing it till it becomes firmly packed.
In the high rise buildings, piles are used for compressing the soil. They are pounded into the soil from some distance, and height, and their goal is to reach the bedrock within the soil. Bedrock is an ideal place to bear the load of the building, as it is hardened by the natural phenomena of settling and the artificial compression process to great extents.
However, small buildings and homes do need to rest on piles, as it is quite expensive to reach the bedrock. Properly compressed substrates even above the surface of the bedrock can bear the load of the building.
The top most layer of the soil contains the highest percentage of composite materials, so excavate the top 2-3 feet of soil to reach a denser surface.
Tamping is a process of compressing the soil really hard indeed. The easiest method to achieve that is to use a power compactor. They come in many sizes and models, and they use vibrations to compact the soil. Weight also matters, but that does not mean that bigger compactors will give better results, it is the pounds per inch that defines the quality of compaction.